1. Field of the Invention
This invention relates to an image forming apparatus such as, e.g., electrophotographic copier, and electrophotographic printer, to a process cartridge detachably attached to the image forming apparatus body, and to an electric contact member suitable to be used in those apparatuses.
Herein, the image forming apparatus is to form images on recording media using electrophotographic image forming process. The image forming apparatus includes, e.g., electrophotographic copier, electrophotographic printer (LED printer, laser beam printer, etc.), electrophotographic facsimile machine, and electrophotographic word processor.
The process cartridge is made of a cartridge integrating an electrophotographic photosensitive drum as an image carrier with at least one of charging means, developing means, and cleaning means, and the cartridge is used as detachably attached to the image forming apparatus body.
2. Description of Related Art
Image forming apparatuses such as photocopiers, printers, and facsimile machines using an transfer type electrophotographic method are conventionally constituted of a photosensitive body as an image carrier typically made in a rotary drum shape, a charging device (charging process) for processing uniformly charging the photosensitive body at a prescribed polarity and potential, an exposing device (exposing process) as information writing means forming electrophotographic latent images on the photosensitive body processed with charging, a developing device (developing process) for visualizing the electrophotographic latent images formed on the photosensitive body with a developing agent, a transferring device (transferring process) for transferring the developing agent images onto a transfer material such as a paper from the surface of the photosensitive body, a cleaning device (cleaning process) cleaning the photosensitive body surface by removing the developing agent remaining more or less on the photosensitive body after the transfer process, and a fixing device (fixing process) for fixing the developing agent image on the transfer material, and the photosensitive body serves for image formation upon applying repeatedly the electrophotographic process (charging, exposing, developing, transferring, cleaning, and fixing).
Although the developing agent remaining on the photosensitive body after the transfer process is removed from the surface of the photosensitive body by the cleaning device and is reserved in the cleaning device as the waste developing agent, it is desirable to nullify such a waste developing agent in terms of environment preservation and effective use of resources. An image forming apparatus returning the remaining developing agent image, or namely so-called-the waste developing agent collected at the cleaning device and reutilizing the agent, has been known.
An image forming apparatus of non-cleaner type has been proposed in which the remaining developing agent image on the photosensitive body after the transfer process is removed by cleaning concurrently done with the development in the developing device and is collected to be reused. A structure, inter alia, has been proposed in which a developing agent charging amount controlling means is used as a charger (developing agent charging means) in the image forming apparatus as to control the charging amount of the developing agent to collect the developing agent at the developing device and reuse the agent.
However, in the image forming apparatus using the developing agent charging amount controlling means as the prior art, where an immobilized blush shape member is used as the developing agent charging amount controlling means and where the triboelectricity of the remaining developing agent image is controlled to be a proper charging amount with a normal polarity, overcharging of the remaining developing agent image may occur locally. If such overcharging of the remaining developing agent image occurs, the mirror reflection force between the photosensitive body and the overcharged developing agent becomes too strong, so that the remaining developing agent image cannot be attached even with a contact charging device, cannot be collected with the developing apparatus, and cannot be transferred with a transferring device, and consequently, the remaining developing agent image is adhered to the surface of the photosensitive body, thereby forming defective images.
It turns out that this phenomenon is caused by an immobilized brush serving as the developing agent charging amount controlling means being positioned continuously at a fixed location on the photosensitive body. That is, where the developing agent charging amount controlling means operates with irregular resistance, overcharging or inadequate charging always occurs at the same location on the photosensitive body. At the charged portion, the problems of localized overcharging or melting of the remaining developing agent image may occur. At the inadequate charging portion, the contact charging member may get dirty due to attachment of the developing agent because the remaining developing agent image cannot be charged adequately.
According to various recent needs of users, the above problems are further raised because a large remaining developing agent image occurs as a result of a continuous printing operation of high printing rate images, such as photographic images or multiple developing methods on the photosensitive body in association with rendering the images in multiple colors.
As a similar case, particles such as dust, floating developing agents, and charged products may attached onto a roller surface after a long period of use because the charging roller used as a charger for the photosensitive body rotates in contact with the photosensitive body. It is to be noted that Japanese Patent Application Publication 2001-215,799 discloses that a developing agent charging amount controlling means as the charger is moved reciprocally in the longitudinal direction of the photosensitive body, but a proper electric contact member is sought to apply a stable voltage to the developing agent charging amount controlling means moving reciprocally.